I think colors are a nice idea... as long as there are options for those who don't want colors. My Mother in law had a 5C, and she really liked it. She wanted a blue one, but when we got to Verizon, there was only a yellow iPhone available. She wasn't pleased, but I found a blue Otterbox Commuter case, and that took care of it. She was happy!
The only issue with colors is that sometimes the choices are not ones that the buyer is happy with. Trendy colors can be a good thing, but not always! I shudder to think of iPhones in the color of trendy colors from the 70's! Can you imagine an avocado or harvest gold iPhone?